Light Scattering from First and Second Sound near the<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>λ</mml:mi></mml:math>Transition in Liquid He

Abstract

We have observed the second-sound contribution to the Brillouin spectrum of liquid ${\mathrm{He}}^{4}$ near the $\ensuremath{\lambda}$ transition at saturated vapor pressure and at 25.1 atm. Its spectral shape is compared with theoretical predictions. We have determined the intensity ratio of second- and first-sound scattering between ${10}^{\ensuremath{-}5}^{\ensuremath{\circ}}\mathrm{K}&lt;{T}_{\ensuremath{\lambda}}\ensuremath{-}T&lt;{10}^{\ensuremath{-}1}^{\ensuremath{\circ}}\mathrm{K}$, and we present data on the dispersion and damping of high-frequency first and second sound.